The present invention relates to an arrester disconnecting device for disconnecting an arrester from an electric circuit when it malfunctions.
FIGS. 4 and 5 show a conventional surge arrester disconnecting device such as disclosed in Japanese Patent Application Laid-Open No. 95284/1980. In these figures, an arrester 1, a gap portion 4 composed of a reactor 2 and a gap 3 and a disconnecting portion 7 composed of a fusible wire 5 and a breaker portion 6 are connected in series through a connecting metal part 8 with a power transmission cable 9. The cable 9 is separately supported by a suspending insulator 10. FIG. 6 is an equivalent circuit of this construction with the arrester 1 and the suspending insulator 10 being shown as electrostatic capacitances.
In FIGS. 4 to 6, when the arrester 1 is operated by high frequency lightning impulse, an impedance of the reactor 2 becomes high, so that surge current does not flow through the fusible wire 5 and thus a voltage is applied across the gap 3. Therefore, lightning impulse current flows through the gap 3, a shunt 11 to the connecting metal, part 8. On the other hand, when the arrester 1 is in an abnormal condition, a grounding current of commercial frequency may flow. However, since the commercial frequency is low, the impedance of the reactor 2 is low enough and thus the grounding current flows through the reactor 2 to the fusible wire 5. When the fusible wire 5 is melted down by the grounding current, an arc is generated in that portion causing pressure in a space inside an insulating tube 12 of the disconnecting portion 7 to be high. With such increase of inner pressure, the insulating tube 12 is broken, resulting in a rapid disconnection of the arrester 1 from the power transmission cable 9.
The conventional arrester disconnecting device includes an explosive destruction of a portion thereof by increase of inner pressure of an insulating tube due to arc produced after a fusible wire is melted down, which is dangerous.